Micromirror devices for use, for example, in optical communications techniques and for optical matrix switches are known in the art. For example, apparatus useful for such communications links is known from U.S. Pat. No. 6,295,154, entitled “Optical Switching Apparatus”, commonly assigned herewith and incorporated herein by reference. This patent discloses a micromirror assembly for directing a light beam in an optical switching apparatus. As disclosed in this patent, which reflects the light beam in a manner that may be precisely controlled by electrical signals, the micromirror assembly includes a silicon mirror capable of rotating in two axes. One or more small magnets are attached to the micromirror itself; a set of four coil drivers are arranged in quadrants, and are controlled to attract or repel the micromirror magnets as desired, to tilt the micromirror in the desired direction.
Micromachined mirrors for two-dimensional scanning at different rates suitable for television display are known, for example, in U.S. Pat. No. 5,629,790. The mirrors may be electrostatically or electromagnetically deflected and rely on the torsional forces in the flexible hinges to restore the mirror to its original position in a resonance scanning technique. The magnetic deflection technique uses a galvanometer type drive in which the coil is formed around the periphery of the mirror and a permanent magnet is provided external to the mirror. The mirrors operate at resonant frequency as shown in Table 1 and can be utilized along with modulated laser light to form television receiver images as a compact substitute for a cathode ray tube.
Copending application Ser. No. 09/957,476 which is commonly owned and which is incorporated herein by reference, provides a micromirror assembly that includes a package and method for making a package having a sensing capability for the position of the micromirror. This package and method is relatively low-cost, and well suited for high-volume production. The package is molded around a plurality of coil drivers, and their control wiring, for example by injection or transfer molding. A two-axis micromirror and magnet assembly is attached to a shelf overlying the coil drivers. Underlying the mirror is a sensor for sensing the angular position of the mirror. According to the preferred embodiment of the invention, the sensor includes a light-emitting diode and angularly spaced light sensors that can sense the intensity of light emitted by the diode and reflecting from the backside of the mirror. The position of the mirror can be derived from a comparison of the intensities sensed by the various angularly positioned light sensors.
It is desirable to have a very small mirror, on the order of 1 mm2, which could be built into a compact package and used for scanning at a vertical scanning frequency of 50 or 60 Hz, for example. This scanning mirror could be used for the vertical deflection in the formation of a television picture, for example. The small dimensions of such a mirror do not provide the space for optical or capacitor sensing devices. Thus, there is a need for a new position sensing device which can be used for such small scanning mirrors, for example. This mirror would not utilize a resonance scanning frequency.